Thin film transistor and display substrate having the same

ABSTRACT

A display substrate includes a base substrate, a semiconductor active layer disposed on the base substrate, a gate insulating layer disposed on the semiconductor active layer, a first conductive pattern group disposed on the gate insulating layer and including at least a gate electrode, a second conductive pattern group insulated from the first conductive pattern group and including at least a source electrode, a drain electrode, and a data pad. The second conductive pattern group includes a first conductive layer and a second conductive layer disposed on the first conductive layer to prevent the first conductive layer from being corroded and oxidized.

CLAIM OF PRIORITY

This application makes reference to, incorporates into thisspecification the entire contents of, and claims all benefits accruingunder 35 U.S.C. §119 from an application earlier filed in the KoreanIntellectual Property Office on Jan. 15, 2013 and there duly assignedSerial No. 10-2013-0004527.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a thin film transistor and a displaysubstrate having the same. More particularly, the present inventionrelates to a thin film transistor applied to an active type displaydevice and a display substrate having the thin film transistor.

2. Description of the Related Art

In general, a display substrate is applied to a flat panel displaydevice, e.g., a liquid crystal display device, an organicelectroluminescent display device, etc., to realize lightweight and thinthickness of the flat panel display device.

The display substrate includes pixels arranged in a matrix form anddisplays an image by applying a source voltage to each pixel. Thedisplay substrate includes gate lines and data lines crossing the gatelines, and the gate lines are insulated from the data lines by aninsulating layer. Each gate line is connected to a thin film transistordisposed in each pixel and applies a signal to the thin film transistorto control the thin film transistor. The thin film transistor switches avoltage applied to a corresponding pixel of the pixels. In addition,each data line applies the voltage to the corresponding pixel of thepixels.

Meanwhile, source and drain electrodes of the thin film transistor andthe data line are formed of a conductive material, such as aluminum,copper, etc. However, aluminum and copper are vulnerable to corrosionand oxidation.

SUMMARY OF THE INVENTION

The present invention provides a thin film transistor capable ofpreventing source and drain electrodes from being corroded.

The present invention provides a display substrate having the thin filmtransistor.

Embodiments of the invention provide a thin film transistor including asemiconductor active layer that includes a source region and a drainregion, a gate electrode insulated from the semiconductor active layer,a source electrode making contact with the source region, and a drainelectrode making contact with the drain region. Each of the source anddrain electrodes includes a first conductive layer that includes one ofcopper, a copper alloy, aluminum, and an aluminum alloy, and a secondconductive layer disposed on the first conductive layer and including amolybdenum-nickel alloy.

The molybdenum-nickel alloy contains nickel of about 10 at % to about 50at % with respect to an aggregate of the molybdenum-nickel alloy.

Each of the source electrode and the drain electrode further includes athird conductive layer disposed under the first conductive layer andincluding a same material as the second conductive layer. The secondconductive layer and the third conductive layer include amolybdenum-nickel-titanium alloy. The molybdenum-nickel-titanium alloycontains nickel of about 15 at % to about 30 at % with respect to anaggregate of the molybdenum-nickel-titanium alloy and titanium of about10 at % to about 20 at % with respect to the aggregate of themolybdenum-nickel-titanium alloy.

Embodiments of the invention provide a display substrate including abase substrate, a semiconductor active layer disposed on the basesubstrate, a first conductive pattern group insulated from thesemiconductor active layer and including at least a gate electrode, asecond conductive pattern group insulated from the first conductivepattern group and including at least a source electrode, a drainelectrode and a data pad, and an organic light emitting device connectedto the drain electrode. The second conductive pattern group includes afirst conductive layer and a second conductive layer disposed on thefirst conductive layer, and the second conductive layer prevents thefirst conductive layer from being corroded and oxidized.

The first conductive layer includes one of copper, a copper alloy,aluminum, and an aluminum alloy, and the second conductive layerincludes a molybdenum-nickel alloy.

The semiconductor active layer includes a semiconductor oxide, and thesemiconductor oxide includes at least one of Zn, In, Ga, Sn, or amixture thereof.

Embodiments of the invention provide a display substrate including abase substrate, a first thin film transistor disposed on the basesubstrate, a second thin film transistor disposed on the base substrateand electrically connected to the first thin film transistor, and anorganic light emitting device connected to the second thin filmtransistor. The first thin film transistor includes a firstsemiconductor active layer, a first gate electrode, a first sourceelectrode, and a first drain electrode, and the second thin filmtransistor includes a second semiconductor active layer, a second gateelectrode, a second source electrode, and a second drain electrode. Thefirst source electrode, the first drain electrode, the second sourceelectrode, and the second drain electrode are disposed on a same layer,and each of the first source electrode, the first drain electrode, thesecond source electrode, and the second drain electrode includes a firstconductive that includes one of copper, a copper alloy, aluminum, and analuminum alloy, and a second conductive layer disposed on the firstconductive layer and including a molybdenum-nickel alloy.

According to the above, each of the source electrode, the drainelectrode, and the data line includes the conductive layer ofmolybdenum-nickel alloy, and thus the source electrode, the drainelectrode, and the data line may be prevented from being corroded andoxidized.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention, and many of the attendantadvantages thereof, will be readily apparent as the same becomes betterunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings, in which likereference symbols indicate the same or similar components, wherein:

FIG. 1 is a circuit diagram showing a flat panel display deviceincluding a display substrate according to an exemplary embodiment ofthe present invention;

FIG. 2 is a plan view showing one pixel shown in FIG. 1;

FIG. 3 is a cross-sectional view taken along a line I-I′ shown in FIG.2;

FIG. 4 is an enlarged view showing a portion PA shown in FIG. 1;

FIG. 5 is a cross-sectional view taken along a line II-II′ shown in FIG.4;

FIG. 6 is a cross-sectional view showing a pixel of a display substrateaccording to another exemplary embodiment of the present invention;

FIG. 7 is a cross-sectional view showing a pad area of a displaysubstrate according to another exemplary embodiment of the presentinvention;

FIG. 8 is a plan view showing a pixel of a display substrate accordingto another exemplary embodiment of the present invention;

FIG. 9 is a cross-sectional view taken along a line II-II′ shown in FIG.8;

FIG. 10 is a cross-sectional view showing a pad area of a displaysubstrate according to another exemplary embodiment of the presentinvention;

FIG. 11 is a plan view showing a pixel of a display substrate accordingto another exemplary embodiment of the present invention;

FIG. 12 is a cross-sectional view taken along a line III-III′ shown inFIG. 11;

FIG. 13 is a cross-sectional view showing a pad area of a displaysubstrate according to another exemplary embodiment of the presentinvention;

FIG. 14 is a view showing an experimental result of corrosion andoxidation of a conductive layer of Mo/Al/Mo under high temperature andmoisture conditions; and

FIG. 15 is a view showing an experimental result of corrosion andoxidation of a conductive layer of Mo—Ni—Ti alloy/Al/Mo—Ni—Ti alloyunder high temperature and moisture conditions.

DETAILED DESCRIPTION OF THE INVENTION

It will be understood that, when an element or layer is referred to asbeing “on”, “connected to” or “coupled to” another element or layer, itcan be directly on, connected or coupled to the other element or layeror intervening elements or layers may be present. In contrast, when anelement is referred to as being “directly on,” “directly connected to”or “directly coupled to” another element or layer, there are nointervening elements or layers present. Like numbers refer to likeelements throughout. As used herein, the term “and/or” includes any andall combinations of one or more of the associated listed items.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, components, regions, layersand/or sections, these elements, components, regions, layers and/orsections should not be limited by these terms. These terms are only usedto distinguish one element, component, region, layer or section fromanother element, component, region, layer or section. Thus, a firstelement, component, region, layer or section discussed below could betermed a second element, component, region, layer or section withoutdeparting from the teachings of the present invention.

Spatially relative terms, such as “beneath”, “below”, “lower”, “above”,“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the exemplary term “below” can encompass both anorientation of above and below. The device may be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms, “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “includes”and/or “including”, when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention applies. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

Hereinafter, the present invention will be explained in detail withreference to the accompanying drawings.

FIG. 1 is a circuit diagram showing a flat panel display deviceincluding a display substrate according to an exemplary embodiment ofthe present invention.

Referring to FIG. 1, a display substrate DS may be applied to a flatpanel display device, such as a liquid crystal display device, anorganic electroluminescent display device, etc. In the present exemplaryembodiment, the organic electroluminescent display device to which thedisplay substrate DS is applied will be described as a representativeexample.

The organic electroluminescent display device includes the displaysubstrate DS including a display part 10, a scan driver 20, and a datadriver 30.

The scan driver 20 and the data driver 30 are electrically connected tothe display part 10 through signal lines. The signal lines include scanlines SL₁, SL₂, and SLn, data lines DL₁, DL₂, and DLm, and sourcevoltage supply lines VL, and any one of the signal lines crosses theother signal lines.

In detail, the scan driver 20 is electrically connected to the displaypart 10 by the scan lines SL₁, SL₂, and SLn. The scan driver 20 appliesscan signals to the display part 10 through the scan lines SL₁, SL₂, andSLn. The scan lines SL₁, SL₂, and SLn are extended in a first directionon the display substrate DS.

The data driver 30 is electrically connected to the data lines DL₁, DL₂,and DLm through a pad (not shown) disposed in a pad area PA of thedisplay substrate DS. Accordingly, the data driver 30 is electricallyconnected to the display part 10 through the data lines DL₁, DL₂, andDLm. The data driver 30 applies data signals to the display part 10through the data lines DL₁, DL₂, and DLm.

The data lines DL₁, DL₂, and DLm are extended in a second directiondifferent from the first direction so as to cross the scan lines SL₁,SL₂, and SLn. Thus, the data lines DL₁, DL₂, and DLm cross the scanlines SL₁, SL₂, and SLn.

The source voltage supply lines VL apply a source voltage to the displaypart 10. The source voltage supply lines VL cross the data lines DL₁,DL₂, and DLm and the scan lines SL₁, SL₂, and SLn.

The display part 10 includes a plurality of pixels PX. Each pixel PX iselectrically connected to a corresponding data line of the data linesDL₁, DL₂, and DLm, a corresponding scan line of the scan lines SL₁, SL₂,and SLn, and a corresponding source voltage supply line of the sourcevoltage supply lines VL. Each pixel PX includes a switching thin filmtransistor TRs, a driving thin film transistor TRd, a capacitor C, andan organic light emitting device OLED.

The switching thin film transistor TRs is connected to a correspondingdata line of the data lines DL₁, DL₂, and DLm and to a correspondingscan line of the scan lines SL₁, SL₂, and SLn. Each of the switchingthin film transistor TRs and the driving thin film transistor TRdincludes a semiconductor active layer, a gate electrode insulated fromthe semiconductor active layer, and source and drain electrodes makingcontact with the semiconductor active layer.

According to the organic electroluminescent display device, the scansignals are applied to the pixels PX through the scan lines SL₁, SL₂,and SLn from the scan driver 20 and the data signals are applied to thepixels PX through the data lines DL₁, DL₂, and DLm from the data driver30. The switching thin film transistor TRs of each pixel PX turns on oroff the driving thin film transistor TRd in response to the scan signaland the data signal. The driving thin film transistor TRd applies adriving current to the organic light emitting device OLED according tothe data signal. The organic light emitting device OLED generates lightusing the driving current.

Meanwhile, the capacitor C, which maintains the data signal during apredetermined time period, is connected between the drain electrode ofthe switching thin film transistor TRs and the gate electrode of thedriving thin film transistor TRd. The data signal charged in thecapacitor C applies the data signal to the gate electrode of the drivingthin film transistor TRd after the switching thin film transistor TRs isturned off.

Although not shown in detail, the organic electroluminescent displaydevice may further include additional thin film transistors andcapacitors in order to compensate for a threshold voltage of the drivingthin film transistor TRd.

Hereinafter, the structure of the display substrate DS will be describedin detail with reference to FIGS. 2 and 3, and a direction in which theswitching thin film transistor TRs, the driving thin film transistor TRdand the organic light emitting device OLED are disposed within thedisplay substrate DS will be referred to as “upper portion”.

FIG. 2 is a plan view showing one pixel shown in FIG. 1, and FIG. 3 is across-sectional view taken along a line I-I′ shown in FIG. 2.

Referring to FIGS. 2 and 3, the pixel PX of the display substrate DS iselectrically connected to the corresponding data line DL₁ of the datalines DL₁, DL₂, and DLm, the corresponding scan line SL₁ of the scanlines SL₁, SL₂, and SLn, and the corresponding source voltage supplyline VL of the source voltage supply lines VL. Each pixel PX includesthe switching thin film transistor TRs, the driving thin film transistorTRd, the capacitor C electrically connected to the switching thin filmtransistor TRs and the driving thin film transistor TRd, and the organiclight emitting device OLED.

The switching thin film transistor TRs is connected to the correspondingdata line DL₁ and the corresponding scan line SL₁. Each switching thinfilm transistor TRs and each driving thin film transistor TRd includesthe semiconductor active layer SA, the gate electrode GE insulated fromthe semiconductor active layer SA, and source and drain electrodes SEand DE making contact with the semiconductor active layer SA.

In more detail, each switching thin film transistor TRs and each drivingthin film transistor TRd includes the semiconductor active layer SA, thegate electrode GE insulated from the semiconductor active layer SA, andsource and drain electrodes SE and DE making contact with thesemiconductor active layer SA, which are disposed on a base substrate100 formed of a transparent glass or plastic material.

The semiconductor active layer SA includes poly-silicon p-Si or oxidesemiconductor. In addition, the semiconductor active layer SA includes asource region making contact with the source electrode SE, a drainregion making contact with the drain electrode DE, and a channel regiondisposed between the source region and the drain region. To this end,the source and drain regions are doped with impurities. The oxidesemiconductor includes at least one of Zn, In, Ga, Sn, or a mixturethereof. For instance, the oxide semiconductor may includeindium-gallium-zinc oxide (IGZO).

Although not shown in the figures, when the semiconductor active layerSA includes the oxide semiconductor, a light blocking layer may bedisposed on and under the oxide semiconductor active layer SA to blockthe light traveling to the oxide semiconductor active layer SA.

Meanwhile, a buffer layer 110 is disposed between the semiconductoractive layer SA and the base substrate 100. The buffer layer 110 may bea silicon oxide layer or a silicon nitride layer, or may have amulti-layer structure of the silicon oxide layer and the silicon nitridelayer. The buffer layer 110 prevents impurities from being diffused tothe switching thin film transistor TRs, the driving thin film transistorTRd, and the organic light emitting device OLED, and prevents moistureor oxygen from being infiltrated into the switching thin film transistorTRs, the driving thin film transistor TRd, and the organic lightemitting device OLED. In addition, the buffer layer 110 planarizes asurface of the base substrate 100.

A gate insulating layer 120 is disposed on the semiconductor activelayer SA and the base substrate 100 to cover the semiconductor activelayer SA and the base substrate 100, and thus the semiconductor activelayer SA and the gate electrode GE are insulated from each other. Thegate insulating layer 120 includes silicon oxide (SiO2) and/or siliconnitride (SiNx).

The scan line SL₁ is disposed on the gate insulating layer 120 andextended in the direction. A portion of the scan line SL₁ is extended tothe pixel PX to serve as the gate electrode GE overlapped with thechannel region of the semiconductor active layer SA.

An inter-insulating layer 130 is disposed on the gate insulating layer120 and the gate electrode GE. The inter-insulating layer 130 includessilicon oxide or silicon nitride as the gate insulating layer 120. Inaddition, the inter-insulating layer 130 is provided with contact holesto expose a portion of the source region and a portion of the drainregion.

The data line DL₁ and the source voltage supply line VL, which cross thescan line SL₁, and the source electrode SE and the drain electrode DE,which are insulated from the gate electrode GE, are disposed on theinter-insulating layer 130. The source electrode SE and the drainelectrode DE make contact with the source region and the drain region,respectively, through the contact holes. The source electrode SE and thedrain electrode DE include a conductive metal and a conductive polymer.

The data line DL₁, the source voltage supply line VL, the sourceelectrode DE, and the drain electrode DE include a first conductivelayer 141 disposed on the inter-insulating layer 130 and a secondconductive layer 145 disposed on the first conductive layer 141. Thesecond conductive layer 145 blocks the diffusion of materials includedin the first conductive layer 141 and prevents the first conductivelayer 141 from being corroded or oxidized. For instance, the firstconductive layer 141 includes copper (Cu), copper alloy (Cu-alloy),aluminum (Al), or aluminum alloy (Al-alloy) and the second conductivelayer 145 includes molybdenum alloy (Mo-alloy). The molybdenum alloyincludes molybdenum-nickel alloy (Mo—Ni alloy) and contains nickel ofabout 10 at % to about 50 at % with respect to an aggregate of themolybdenum-nickel alloy.

The capacitor C includes a first capacitor electrode C₁ and a secondcapacitor electrode C₂.

The first capacitor electrode C₁ is formed of the same material as, anddisposed on the same layer as, the scan lines SL₁, SL₂, and SLn and thegate electrode GE. That is, the first capacitor electrode C₁ is disposedon the gate insulating layer 120.

The second capacitor electrode C₂ is formed of the same material as, anddisposed on the same layer as, the data line DL₁, the source voltagesupply line VL, the source electrode SE, and the drain electrode DE.That is, the second capacitor electrode C₂ is disposed on theinter-insulating layer 130 and has a double-layer structure of the firstconductive layer 141 and the second conductive layer 145. In this case,one of the first and second conductive layers 141 and 145 may be removedfrom the second capacitor electrode C₂.

A protective layer 150 is disposed on the switching thin film transistorTRs, the driving thin film transistor TRd, and the capacitor C. Theprotective layer 150 may include at least one layer. In detail, theprotective layer 150 includes an inorganic protective layer and anorganic protective layer disposed on the inorganic protective layer. Theinorganic protective layer includes at least one of silicon oxide orsilicon nitride. In addition, the organic protective layer includesacryl, polyimide, polyamide, or benzocyclobutene. That is, the organicprotective layer may have transparency and fluidity to planarize a lowerlayer thereof.

The organic light emitting device OLED is disposed on the protectivelayer 150. In addition, the organic light emitting device OLED includesa first electrode 160 making contact with the drain electrode DE of thedriving thin film transistor TRd, a pixel definition layer PDL exposinga portion of the first electrode 160, an organic layer 170 disposed onthe exposed portion of the first electrode 160, and a second electrode180 disposed on the organic layer 170. Here, one of the first electrode160 and the second electrode 180 is an anode electrode and the other oneof the first electrode 160 and the second electrode 180 is a cathodeelectrode. In the present exemplary embodiment, the first electrode 160serves as the anode electrode and the second electrode 180 serves as thecathode electrode.

The first electrode 160 includes a transparent conductive oxide, e.g.,indium tin oxide (ITO), indium zinc oxide (IZO), aluminum zinc oxide(AZO), gallium-doped zinc oxide (GZO), zinc tin oxide (ZTO), gallium tinoxide (GTO), fluorine-doped tin oxide (FTO), etc. The first electrode160 may include a semi-transparent reflective layer to improve a lightemitting efficiency of the organic light emitting device OLED.

The organic layer 170 is disposed on the portion of the first electrode160 exposed by the pixel definition layer PDL. The organic layer 170includes at least a light emitting layer EML and may have a multi-layerstructure. For instance, the organic layer 170 includes a hole injectionlayer (HIL) that injects holes, a hole transport layer (HTL) thatcontrols electrons, which are not combined with the holes in the lightemitting layer EML, to enhance combination opportunities between theholes and the electrons, the light emitting layer EML that emits lightusing recombination of the holes and the electrons, a hole blockinglayer (HBL) that controls movement of the holes not combined with theelectrons, an electron transport layer (ETL) that transports theelectrons to the light emitting layer EML, and an electron injectionlayer (EIL) that injects the electrons.

In addition, the light emitted from the organic layer 170 has one ofred, green, blue, and white colors. For instance, when the organic lightemitting device OLED is an RGB type, the color of the light emittingfrom the organic layer 170 of each pixel PX is one of the red, green,and blue colors. In addition, the organic light emitting device OLED isa WOLED type, the color of the light emitting from the organic layer 170of each pixel PX being white. In the present exemplary embodiment, thecolor of the light emitted from the organic layer 170 is red, green,blue or white, but it should not be limited thereto or thereby. That is,the color of the light emitted from the organic layer 170 may bemagenta, cyan, or yellow.

The second electrode 180 may include at least one of Mo, MoW, Cr, Al,AlNd, or aluminum alloy, has a work function lower than that of thefirst electrode 160, and reflects light.

In the present exemplary embodiment, the light emitted from the organiclayer 170 travels to the first electrode 160, but it should not belimited thereto or thereby. For instance, in a case wherein the firstelectrode 160 includes a reflective layer (not shown) to reflect thelight generated by the organic layer 170, and the second electrode 180transmits the light, the light generated by the organic layer 170 maytravel to the second electrode 180.

FIG. 4 is an enlarged view showing a pad area PA shown in FIG. 1 andFIG. 5 is a cross-sectional view taken along a line II-II′ shown in FIG.4.

Referring to FIGS. 4 and 5, a data pad PD is disposed in the pad area PAof the display substrate DS of FIG. 1 and is electrically connected tothe data line DL₁.

The data pad PD has the same structure as the data line DL₁. In detail,the data pad PD includes the first conductive layer 141 disposed on theinter-insulating layer 130 and the second conductive layer 145 disposedon the first conductive layer 141. The second conductive layer 145blocks the diffusion of materials included in the first conductive layer141 and prevents the first conductive layer 141 from being corroded oroxidized. For instance, the first conductive layer 141 includes copper(Cu), copper alloy (Cu-alloy), aluminum (Al), or aluminum alloy(Al-alloy) and the second conductive layer 145 includes molybdenum alloy(Mo-alloy). The molybdenum alloy includes molybdenum-nickel alloy (Mo—Nialloy) and contains nickel of about 10 at % to about 50 at % withrespect to an aggregate of the molybdenum-nickel alloy.

Hereinafter, a pixel of a display substrate will be described withreference to FIGS. 6 to 13 according to exemplary embodiments of thepresent invention. In FIGS. 6 to 13, the same reference numerals denotethe same elements in as seen in FIGS. 1 to 5, and thus detaileddescriptions of the same elements will be omitted.

FIG. 6 is a cross-sectional view showing a pixel of a display substrateaccording to another exemplary embodiment of the present invention, andFIG. 7 is a cross-sectional view showing a pad area of a displaysubstrate according to another exemplary embodiment of the presentinvention.

Referring to FIGS. 6 and 7, each pixel of the display substrate DSincludes a switching thin film transistor TRs, a driving thin filmtransistor TRd, a capacitor C electrically connected to the switchingthin film transistor TRs and the driving thin film transistor TRd, andan organic light emitting device OLED making electrical contact with thedriving thin film transistor TRd. In addition, a data pad PD is disposedin the pad area PA of the display substrate DS so as to be electricallyconnected to the data line DL₁.

The switching thin film transistor TRs is connected to the scan line SL₁and the data line DL₁ and the driving thin film transistor TRd isconnected to the capacitor C and the source voltage supply line VL. Eachof the switching thin film transistor TRs and the driving thin filmtransistor TRd includes a semiconductor active layer SA, a gateelectrode GE insulated from the semiconductor active layer SA, andsource and drain electrodes SE and DE making contact with thesemiconductor active layer SA.

Each of the data line DL₁, the source voltage supply line VL, the sourceelectrode SE, the drain electrode DE, and the data pad PD includes thefirst conductive layer 141 disposed on the inter-insulating layer 130,the second conductive layer 145 disposed on the first conductive layer141, and a third conductive layer 147 disposed under the firstconductive layer 141.

The first conductive layer 141 includes one of copper (Cu), copper alloy(Cu-alloy), aluminum (Al), and aluminum alloy (Al-alloy).

The second and third conductive layers 145 and 147, respectively, mayhave the same material. The second and third conductive layers 145 and147, respectively, block the diffusion of materials included in thefirst conductive layer 141 and prevent the first conductive layer 141from being corroded or oxidized. The second and third conductive layers145 and 147, respectively, may include molybdenum alloy (Mo-alloy). Themolybdenum alloy may be molybdenum(Mo)-nickel(Ni)-titanium(Ti) alloy.The molybdenum alloy contains nickel of about 15 at % to about 30 at %with respect to an aggregate of the molybdenum alloy and titanium ofabout 10 at % to about 20 at % with respect to the aggregate of themolybdenum alloy.

The capacitor C includes a first capacitor electrode C₁ and a secondcapacitor electrode C₂. The first capacitor electrode C₁ is formed ofthe same material as, and is disposed on the same layer as, the scanline SL₁ and the gate electrode GE.

The second capacitor electrode C₂ is formed of the same material as, andis disposed on the same layer as, the data line DL₁, the source voltagesupply line VL, the source electrode SE, and the drain electrode DE.That is, the second capacitor electrode C₂ includes the first conductivelayer 141 disposed on the inter-insulating layer 130, the secondconductive layer 145 disposed on the first conductive layer 141, and thethird conductive layer 147 disposed under the first conductive layer141.

In addition, the organic light emitting device OLED includes the firstelectrode 160 making contact with the drain electrode DE of the drivingthin film transistor TRd, the pixel definition layer PDL exposing theportion of the first electrode 160, the organic layer 170 disposed onthe exposed portion of the first electrode 160, and the second electrode180 disposed on the organic layer 170.

FIG. 8 is a plan view showing a pixel of a display substrate accordingto another exemplary embodiment of the present invention, FIG. 9 is across-sectional view taken along a line II-II′ shown in FIG. 8, and FIG.10 is a cross-sectional view showing a pad area of a display substrateaccording to another exemplary embodiment of the present invention.

Referring to FIGS. 8 to 10, each pixel of the display substrate DS iselectrically connected to the data line DL₁, the scan line SL₁, and thesource voltage supply line VL. Each pixel includes a switching thin filmtransistor TRs, a driving thin film transistor TRd, a capacitor Celectrically connected to the switching thin film transistor TRs and thedriving thin film transistor TRd, and an organic light emitting deviceOLED making electrical contact with the driving thin film transistorTRd. In addition, a data pad PD is disposed in the pad area PA of thedisplay substrate DS so as to be electrically connected to the data lineDL₁.

The switching thin film transistor TRs is connected to the scan line SL₁and the data line DL₁ and the driving thin film transistor TRd isconnected to the capacitor C and the source voltage supply line VL. Oneof the switching thin film transistor TRs and the driving thin filmtransistor TRd, e.g., the switching thin film transistor TRs, may have atop gate structure, and the other one of the switching thin filmtransistor TRs and the driving thin film transistor TRd, e.g., thedriving thin film transistor TRd, may have a bottom gate structure.

The switching thin film transistor TRs includes a first semiconductoractive layer SA1 disposed on the base substrate 100, a first gateelectrode GE1 insulated from the first semiconductor active layer SA1,and a first source electrode SE1 and a first drain electrode DE1 whichmake contact with the first semiconductor active layer SA1.

The driving thin film transistor TRd includes a second gate electrodeGE2 disposed on the gate insulating layer 120, a second semiconductoractive layer SA2 insulated from and overlapped with the second gateelectrode GE, and a second source electrode SE2 and a second drainelectrode DE2 which make contact with the second semiconductor activelayer SA2.

The capacitor C includes a first capacitor electrode C₁ and a secondcapacitor electrode C₂.

In detail, a buffer layer 110 is disposed on the base substrate 100 andthe first semiconductor active layer SA1 is disposed on the buffer layer110.

The first semiconductor active layer SA1 includes poly-silicon (p-Si) oroxide semiconductor. In the present exemplary embodiment, the firstsemiconductor active layer SA1 includes poly-silicon (p-Si).

A gate insulating layer 120 is disposed on the first semiconductoractive layer SA1 and the buffer layer 110 so as to cover the firstsemiconductor active layer SA1, so that the first semiconductor activelayer SA1 is insulated from the first gate electrode GE1.

The scan line SL₁, the first gate electrode GE1 extended from the scanline SL1 and overlapped with the channel region of the firstsemiconductor active layer SA1, the first capacitor electrode C₁, andthe second gate electrode GE2 are disposed on the gate insulating layer120.

A first inter-insulating layer 131 is disposed on the first gateelectrode GE1, the first capacitor electrode C1, the second gateelectrode GE2, and the gate insulating layer 120.

A second semiconductor active layer SA2 is disposed on the firstinter-insulating layer 131 so as to overlap with the second gateelectrode GE2. That is, the first inter-insulating layer 131 serves asthe gate insulating layer of the driving thin film transistor TRd. Inaddition, the second semiconductor active layer SA2 includes amorphoussilicon (a-Si) or oxide semiconductor. For instance, the secondsemiconductor active layer SA2 includes oxide semiconductor, and theoxide semiconductor includes at least one of Zn, In, Ga, Sn, or amixture thereof.

A second inter-insulating layer 135 is disposed on the secondsemiconductor active layer SA2 and the first inter-insulating layer 131.

The data line DL₁, the source voltage supply line VL, the first sourceelectrode SE1, the first drain electrode DE1, the second capacitorelectrode C2, the second source electrode SE2, and the second drainelectrode DE2 are disposed on the second inter-insulating layer 135.

Each of the first source electrode SE1, the first drain electrode DE1,the second capacitor electrode C2, the data line DL1, the source voltagesupply line VL, the second source electrode SE2, the second drainelectrode DE2, and the data pad PD includes a first conductive layer 141disposed on the second inter-insulating layer 131 and a secondconductive layer 145 disposed on the first conductive layer 141. Here,the second conductive layer 145 blocks the diffusion of materialsincluded in the first conductive layer 141 and prevents the firstconductive layer 141 from being corroded or oxidized. For instance, thefirst conductive layer 141 includes copper (Cu), copper alloy(Cu-alloy), aluminum (Al), or aluminum alloy (Al-alloy) and the secondconductive layer 145 includes molybdenum alloy (Mo-alloy). Themolybdenum alloy includes molybdenum-nickel alloy (Mo—Ni alloy) andcontains nickel of about 10 at % to about 50 at % with respect to anaggregate of the molybdenum-nickel alloy.

In addition, the organic light emitting device OLED includes the firstelectrode 160 making contact with the drain electrode DE of the drivingthin film transistor TRd, the pixel definition layer PDL exposing aportion of the first electrode 160, the organic layer 170 disposed onthe exposed portion of the first electrode 160, and the second electrode180 disposed on the organic layer 170.

FIG. 11 is a plan view showing a pixel of a display substrate accordingto another exemplary embodiment of the present invention, FIG. 12 is across-sectional view taken along a line III-III′ shown in FIG. 11, andFIG. 13 is a cross-sectional view showing a pad area of a displaysubstrate according to another exemplary embodiment of the presentinvention.

Referring to FIGS. 11 to 13, each pixel PX of the display substrate DSis electrically connected to the data line DL₁, the scan line SL₁, andthe source voltage supply line VL. Each pixel PX includes a switchingthin film transistor TRs, a driving thin film transistor TRd, acapacitor C electrically connected to the switching thin film transistorTRs and the driving thin film transistor TRd, and an organic lightemitting device OLED making electrical contact with the driving thinfilm transistor TRd. In addition, a data pad PD is disposed in the padarea PA of the display substrate DS so as to be electrically connectedto the data line DL₁.

The switching thin film transistor TRs is connected to the scan line SL₁and the data line DL₁ and the driving thin film transistor TRd isconnected to the capacitor C and the source voltage supply line VL. Boththe switching thin film transistor TRs and the driving thin filmtransistor TRd may have a bottom gate structure.

The switching thin film transistor TRs and the driving thin filmtransistor TRd include a semiconductor active layer SA, a gate electrodeGE insulated from the semiconductor active layer SA, and a sourceelectrode SE and a drain electrode DE which make contact with thesemiconductor active layer SA.

The capacitor C includes a first capacitor electrode C₁ and a secondcapacitor electrode C₂.

Each of the data line DL₁, the source voltage supply line VL, the sourceelectrode SE, the drain electrode DE, and the data pad PD includes firstconductive layer 141 disposed on the inter-insulating layer 130, secondconductive layer 145 disposed on the first conductive layer 141, andthird conductive layer 147 disposed under the first conductive layer141.

The first conductive layer 141 includes copper (Cu), copper alloy(Cu-alloy), aluminum (Al), or aluminum alloy (Al-alloy).

The second conductive layer 145 and the third conductive layer 147include the same material. The second and third conductive layers 145and 147, respectively, block the diffusion of materials included in thefirst conductive layer 141, and prevent the second conductive layer 145from being corroded or oxidized. The second and third conductive layers145 and 147, respectively, include molybdenum alloy (Mo-alloy). Themolybdenum alloy includes molybdenum-nickel-titanium alloy (Mo—Ni—Tialloy) and contains nickel of about 15 at % to about 30 at % withrespect to an aggregate of the molybdenum alloy and titanium of about 10at % to about 20 at % with respect to the aggregate of the molybdenumalloy.

In addition, the organic light emitting device OLED includes firstelectrode 160 making contact with the drain electrode DE of the drivingthin film transistor TRd, pixel definition layer PDL exposing a portionof the first electrode 160, organic layer 170 disposed on the exposedportion of the first electrode 160, and second electrode 180 disposed onthe organic layer 170.

FIG. 14 is a view showing an experimental result of corrosion andoxidation of a conductive layer of Mo/Al/Mo under high temperature andmoisture conditions, and FIG. 15 is a view showing an experimentalresult of corrosion and oxidation of a conductive layer of Mo—Ni—Tialloy/Al/Mo—Ni—Ti alloy under high temperature and moisture conditions.

Referring to FIG. 14, when the conductive layer having the structure ofMo/Al/Mo is exposed to the conditions of a temperature of about 85degrees and an absolute humidity of about 85 percent during about 240hours, corrosion occurs in the conductive layer.

Referring to FIG. 15, when the conductive layer having the structure ofMo—Ni—Ti alloy/Al/Mo—Ni—Ti alloy is exposed to the conditions of thetemperature of about 85 degrees and the absolute humidity of about 85percent during about 240 hours, corrosion does not occur in theconductive layer.

That is, the Al layer is prevented from being corroded by the Mo—Ni—Tialloy disposed on and under the Al layer.

Although exemplary embodiments of the present invention have beendescribed, it is understood that the present invention should not belimited to these exemplary embodiments but various changes andmodifications can be made by one of ordinary skill in the art within thespirit and scope of the present invention as hereinafter claimed.

What is claimed is:
 1. A thin film transistor, comprising: asemiconductor active layer including a source region and a drain region;a gate electrode insulated from the semiconductor active layer; a sourceelectrode contacted with the source region; and a drain electrodecontacted with the drain region, each of the source and drain electrodescomprising: a first conductive layer including one of copper, a copperalloy, aluminum, and an aluminum alloy; and a second conductive layerdisposed on the first conductive layer and including a molybdenum-nickelalloy.
 2. The thin film transistor of claim 1, wherein themolybdenum-nickel alloy contains nickel of about 10 at % to about 50 at% with respect to an aggregate of the molybdenum-nickel alloy.
 3. Thethin film transistor of claim 1, wherein each of the source electrodeand the drain electrode further comprises a third conductive layerdisposed under the first conductive layer and including a same materialas the second conductive layer.
 4. The thin film transistor of claim 3,wherein the second conductive layer and the third conductive layercomprise a molybdenum-nickel-titanium alloy.
 5. The display apparatus ofclaim 4, wherein the molybdenum-nickel-titanium alloy contains nickel ofabout 15 at % to about 30 at % with respect to an aggregate of themolybdenum-nickel-titanium alloy, and titanium of about 10 at % to about20 at % with respect to the aggregate of the molybdenum-nickel-titaniumalloy.
 6. A display substrate, comprising: a base substrate; asemiconductor active layer disposed on the base substrate; a firstconductive pattern group insulated from the semiconductor active layerand including at least a gate electrode; a second conductive patterngroup insulated from the first conductive pattern group and including atleast a source electrode, a drain electrode, and a data pad; and anorganic light emitting device connected to the drain electrode; thesecond conductive pattern group comprising a first conductive layer anda second conductive layer disposed on the first conductive layer toprevent the first conductive layer from being corroded and oxidized. 7.The display substrate of claim 6, wherein the first conductive layercomprises one of copper, a copper alloy, aluminum, and an aluminumalloy.
 8. The display substrate of claim 7, wherein the secondconductive layer comprises a molybdenum-nickel alloy.
 9. The displaysubstrate of claim 8, wherein the molybdenum-nickel alloy containsnickel of about 10 at % to about 50 at % with respect to an aggregate ofthe molybdenum-nickel alloy.
 10. The display substrate of claim 8,wherein the second conductive pattern group further comprises a thirdconductive layer disposed under the first conductive layer and includinga same material as the second conductive layer.
 11. The displaysubstrate of claim 10, wherein the second conductive layer and the thirdconductive layer comprise a molybdenum-nickel-titanium alloy.
 12. Thedisplay substrate of claim 11, wherein the molybdenum-nickel-titaniumalloy contains nickel of about 15 at % to about 30 at % with respect toan aggregate of the molybdenum-nickel-titanium alloy, and titanium ofabout 10 at % to about 20 at % with respect to the aggregate of themolybdenum-nickel-titanium alloy.
 13. The display substrate of claim 6,wherein the semiconductor active layer comprises a semiconductor oxide.14. The display substrate of claim 13, wherein the semiconductor oxidecomprises at least one of Zn, In, Ga, Sn, and a mixture thereof.
 15. Adisplay substrate comprising: a base substrate; a first thin filmtransistor disposed on the base substrate; a second thin film transistordisposed on the base substrate and electrically connected to the firstthin film transistor; and an organic light emitting device connected tothe second thin film transistor; wherein the first thin film transistorcomprises a first semiconductor active layer, a first gate electrode, afirst source electrode, and a first drain electrode; wherein the secondthin film transistor comprises a second semiconductor active layer, asecond gate electrode, a second source electrode, and a second drainelectrode; wherein the first source electrode, the first drainelectrode, the second source electrode, and the second drain electrodeare disposed on a same layer; and wherein each of the first sourceelectrode, the first drain electrode, the second source electrode, andthe second drain electrode comprises: a first conductive layer thatincludes one of copper, a copper alloy, aluminum, and an aluminum alloy;and a second conductive layer disposed on the first conductive layer andincluding a molybdenum-nickel alloy.
 16. The display substrate of claim15, further comprising a third conductive layer disposed under the firstconductive layer and including a same material as the second conductivelayer.
 17. The display substrate of claim 16, wherein the secondconductive layer and the third conductive layer comprise amolybdenum-nickel-titanium alloy.
 18. The display substrate of claim 16,wherein at least one of the first semiconductor active layer and thesecond semiconductor active layer comprises a semiconductor oxide. 19.The display substrate of claim 18, wherein the semiconductor oxidecomprises at least one of Zn, In, Ga, Sn, and a mixture thereof.
 20. Thedisplay substrate of claim 15, further comprising: a gate insulatinglayer disposed between the first semiconductor active layer and thefirst gate electrode, and between the second semiconductor active layerand the second gate electrode; and an inter-insulating layer disposed onthe gate electrode; wherein the first and second semiconductor activelayers are disposed on the base substrate.
 21. The display substrate ofclaim 15, further comprising: a gate insulating layer disposed betweenthe first semiconductor active layer and the first gate electrode; afirst inter-insulating layer that covers the first gate electrode; and asecond inter-insulating layer disposed on the first inter-insulatinglayer; wherein the first semiconductor active layer is disposed on thebase substrate, the first and second gate electrodes are disposed on thegate insulating layer, and the second semiconductor active layer isdisposed on the first inter-insulating layer.
 22. The display substrateof claim 15, further comprising a gate insulating layer disposed betweenthe first semiconductor active layer and the first gate electrode andbetween the second semiconductor active layer and the second gateelectrode, wherein the first and second semiconductor active layers aredisposed on the gate insulating layer.